Fix this sparse warnings:
  drivers/media/dvb/frontends/drx397xD_fw.h:21:2: warning: Using plain integer as NULL pointer
  drivers/media/dvb/frontends/drx397xD_fw.h:22:2: warning: Using plain integer as NULL pointer
Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Acked-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
 } fw[] = {
 #define _FW_ENTRY(a, b, c)     {                                       \
                        .name   = a,                                    \
-                       .file   = 0,                                    \
+                       .file   = NULL,                                 \
                        .lock   = __RW_LOCK_UNLOCKED(fw[c].lock),       \
                        .refcnt = 0,                                    \
                        .data   = { }           }